As the defrosting performance of air conditioning system of a certain car cannot meet the national standard, the energy consumption of air conditioning system is high and the vision of driver is seriously affected. In this chapter, CFD software is used to analyze the steady state and transient state of defrosting in the cockpit air conditioning system of a certain car. It is concluded that there is a phenomenon of streamline swirl in the air duct, the air distribution on the front windshield is uneven, and there is a low speed or zero speed area in the middle of the glass. The defrosting time of this part of the vision area is too long, which seriously affects the driver’s vision. Through adjusting the structure of defrosting air duct and air outlet grille, the inflection point mode of air duct and grille diversion structure are changed, the surface airflow distribution of front windshield is optimized, the wind speed of stall zone is increased, the defrosting effect of each vision zone is significantly improved, the defrosting performance is improved, and the energy consumption of air conditioning system is further optimized. Therefore, the research results are a feasible choice for the design improvement of defrosting structure of the vehicle model.